Dynamic Adaptive Streaming over HTTP (DASH) is a timeline driven technology requiring a very tight synchronization between a client and a server for dynamic or live content streaming. For example, DASH is defined in ISO 23009-1 and 3GPP TS 26.247 V11.1.0 (2012-12). DASH over evolved Multimedia Broadcast and Multicast Services (eMBMS) is defined, for example, in 3GPP TS 26.346 V11.3.0 (2012-12).
The client may receive a media description, for example a Media Presentation Description (MPD), and consecutive media segments. The MDP describes media segment-related information, including media segment timing information that permits synchronization between the server and its client or clients.
The client can be a terminal and the streaming can be a video. In a case the client is requesting a media segment that has not been generated yet by the server and there is no means to get the synchronization back, the client will keep requesting the media segment not being generated yet and will never play the video. In a different case the client may request old media segments, i.e., media segments which have already been sent by the server, then either the media segments are still available and the client will play with a certain delay or the media segments are already obsolete and removed from the server and no video will be played.
In a unicast scenario, when synchronization between the client and the server gets lost, the client may fetch a fresh MPD to re-establish synchronization. Fetching a fresh MPD is, however, not possible in a broadcast scenario.
Some Live Encoders (LE) frequently generate MPDs, for example up to one MPD is generated per every media segment duration. Whenever something goes wrong [deviation/malfunctioning] with the LE, i.e., in the case of an encoder functionality issue, a new MPD is generated. Also, when instead of the segment number the media play time is used as index, the Live Encoder/Segmenter may frequently update the MPD. In a unicast case where the MPD can be fetched frequently, any issue with the LE functionality will be overcome easily with a new download of the MPD file.
However, in a case of broadcast only one version of the MPD is sent towards the client. The system side may send an updated MPD, but it needs to detect that the update is necessary.